The needs of wireless communication have increased dramatically in the last few years. In the meantime, higher data rates are also demanded increasingly. Since the amount of available radio-frequency (RF) spectrum is limited, telecommunication equipment manufacturers are seeking ways to increase the spectral efficiency by using more complex modulation schemes and/or to utilizing available bandwidth at higher RF frequencies.
One of the methods of solving the above-mentioned problems is to use quadrature signals, which have become essential elements in low intermediate frequency (IF) transceivers for today's wireless communication systems. The quadrature signals are typically generated by quadrature voltage controlled oscillator (QVCO) circuits. The quadrature signals allow for quadrature amplitude modulation (QAM), which permits significantly more information to be carried by a particular bandwidth than other modulation schemes such as amplitude modulation (AM) and phase modulation (PM).
There were various types of QVCO circuits. Conventional QVCO circuits, however, often require extra active devices that introduce additional phase noise into the QVCO circuits. In addition, conventional QVCO circuits often suffer from high power consumption, voltage headroom dissipation, and LC resonant frequency effects.